1. Field of the Invention
The present invention relates generally to a die cutting press, and more particularly to a registration system for registering defined areas of web, strip or sheet material with a die unit provided on the press in order to permit accurate processing of the material.
2. Discussion of the Prior Art
A die cutting press is disclosed in U.S. Pat. No. 4,555,968, to Raney. The press disclosed in U.S. Pat. No. 4,555,968 has a shiftable die unit supported on a cushion of air, and the die unit is movable laterally of the direction of travel of the web or strip as well as rotatably about an upright axis perpendicular to the material in order to bring the die unit into precise registration with defined areas of the material to be processed or cut by the press.
Automatic operation of this known press is provided by a control system having two groups of photo-optical sensors which are disposed to detect the presence of two T-shaped marks provided on opposite sides of the material adjacent each defined area to be cut. The control system is electrically coupled to servomotor mechanisms for adjustably positioning the die unit once advancement of the material is interrupted and a defined area on the material is in general proximity to work structure of the press die unit.
As shown in U.S. Pat. No. 4,697,485, to Raney, a die cutting press is provided with a registration system which is operable to provide precise alignment of a shiftable die cutting unit along two axes during the time that the material is advanced along a third axis toward the die unit, so that as soon as a defined area of the material reaches the die unit, the press can be immediately actuated to subject the material to the die cutting operation. Continuous monitoring of an elongated indicator strip provided on the material enables the die unit to be shifted as necessary during travel to insure lateral and angular registration prior to the time that material advancement is interrupted.
As disclosed in U.S. Pat. No. 5,212,647, to Raney, a die cutting press is provided with a registration system that quickly and accurately aligns defined areas of a web or strip of material with a movable die unit without requiring the use of elaborate or continuous marks of more than two sensing devices for determining the location of the marks relative to the die unit. The registration system employs a pair of reference indicia fixed on a bolster of the press for indicating the position at which the indicia on the strip of material appear when the defined areas of the material are in a desired predetermined relationship relative to the die unit supported on the bolster.
Although the accuracy provided by the known prior art registration systems is very good, such presses are relatively slow, being able to operate at speeds no faster than about 20 strokes per minute. Accordingly, it would be desirable to provide a registration system that maintains the accuracy of the known constructions while enabling much faster operation.